Thermal chamber for a developability regulating apparatus

ABSTRACT

An apparatus in which the developability of an electrophotographic printing machine is regulated. Errors induced by temperature fluctuations are minimized by controlling the thermal environment.

United States Patent [191 Whited 1 THERMAL CHAMBER FOR A DEVELOPABILITY REGULATING APPARATUS [75] Inventor: Charles A. Whited, Rochester, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Oct. 6, 1972 [21] Appl. No.: 295,775

[52] US. Cl. 355/3 DD, 117/175, 118/637, 250/238, 355/10 [51] Int. Cl G03g 15/00 [58] Field of Search 355/10, 3 DD; 250/238; 356/201-203; 118/637; 117/175 [56] References Cited UNITED STATES PATENTS 3,327,126 6/1967 Shannon et a1. 250/238 June 18, 1974 3,348,521 10/1967 Hawk 118/637 3,376,854 4/1968 Kamola 118/637 3,421,009 1/1969 Caruthers 250/238 3,553,464 1/1971 Abe 356/201 3,610,205 10/1971 Rarey et a1. 356/201 OTHER PUBLICATIONS Stabilized Temperature Chambers" 3-1968, Products Note No. 2, EG&G Inc., Boston, Mass.

Primary ExaminerRichard L. Moses Attorney, Agent, or Firm-H. Fleischer; James J. Ralabate; C. A. Green [57] ABSTRACT An apparatus in which the developability of an electrophotographic printing machine is regulated. Errors induced by temperature fluctuations are minimized by controlling the thermal environment.

6 Claims, 5 Drawing Figures BACKGROUND OF THE INVENTION This invention relates generally to an electrophotographic printing machine, and more particularly concerns means for maintaining the thermal environment of a photosensor utilized in a developability regulating apparatus substantially at a predetermined temperature in-order to minimize system errors.

In the process of electrophotographic printing a developer mix of carrier granules and toner particles is used to form a toner powder image of an original document on sheet material. The developability regulating apparatus adjusts the characteristics of the developer mix to produce toner powder images having suitable density and color balance, i.e., developability. Developability is related to the concentration of toner particles in the developer'mix, i.e., the ratio of toner particles to carrier granules. Environmental conditions such as temperature and humidity conditions effect developability. The physical parameters of the development system also effect developability, e.g., spacing, electrical bias, mass flow rate and the magnetic field, amongst others. Furthermore, the electrical attraction between the toner particles and carrier granules influences developability. Toner particle concentration within the developer mix is controlled to maintain image density and color balance at an appropriate level.'A system utilizing the developability apparatus of the present invention is described, in detail, in copending application Ser. No. 213,056, filed on Dec. 28, 1971 now US. Pat. No. 3,754,821 and assigned to the assignee of the present invention.

The thermal environment surrounding the photosensor is subject to temperature transients. This is due, in part, to localized heating by such sub-components as the fuser which is incorporated in the printing machine to permanently fix the powder image to the support material. Moreover, heat from scan lamps and electrical power supplies, as well as the air flow generated by the blowers produce thermal transients which may rapidly change the temperature in the region surrounding the photosensor. Photosensors utilized in developability regulating apparatus are frequently sensitive to temperature variations. For example, a 4 C change in the photosensor temperature causes the developability regulating mechanism to indicate that there is an incorrect concentration of toner particles in the developer mix.

It is, therefore, aprimary object of the present invention to improve the thermal environment of the photosensor incorporated in the developability regulating apparatus of electrophotographic printing machine.

SUMMARY OF THE INVENTION Briefly stated, an in accordance with the present invention, there is provided an apparatus for maintaining the thermal environment of a photosensor substantially at a predetermined temperature.

This is accomplished in the present instance by an openeded container defining an internal chamber for housing the photosensor therein. One of the features of the present invention is to transmit light rays to the photosensor by means of a fiber optic light pipe. Hence, in the preferred embodiment, provision is made in an end cap of the container to accommodate the light pipe. The end cap forms, in conjunction with the light pipe, a substantially heat-tight joint. Means are provided for heating the container to a predetermined temperature, and for controlling the heating means such that the container remains substantially at the predetermined temperature.

The present invention is also concerned with minimizing errors due to thermal variations in the photosensor used in the developability regulating apparatus of an electrophotographic printing machine. In performing this function, the photosensor detects modulated light rays to indicate the density of toner particles electrostatically adhering to transparent electrode means. This corresponds to the density of toner particles being deposited on an electrostatic latent image recorded on a photoconductive member. In order to minimize errors in the regulating apparatus, the photosensor is disposed in a thermally controlled environment. Hence, the photosensor is housed in the previously discussed container and is maintained substantially at a predetermined temperature.

' BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 is a schematic perspective view of an electrophotographic printing machine embodying the features of the present invention therein;

FIG. 2 is a sectional elevational view of a photoconductive drum used in the FIG. 1 printing machine, and showing, in detail, the apparatus of the present invention;

FIG. 3 is a sectional elevational view of the apparatus of the present invention;

FIG. 4 is an enlarged, exploded perspective view of the photosensor mounting arrangement incorporated in the FIG. 3 apparatus; and

FIG. 5 is an enlarged, perspective view of the FIG. 4 mounting arrangement.

While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings wherein like reference numerals have been used throughout to designate like elements, FIG. 1 schematically illustrates an electrophotographic printing machine adapted to reproduce multi-color copies from a colored original document. The printing machine depicted in FIG. 1 utilizes a photoconductive member having a rotatably mounted drum 10 with a photoconductive surface 12. Drum 10 is arranged to rotate in the direction of arrow 14 and moves photoconductive surface 12 sequentially through processing stations A through E, inclusive.

Drum 10 initially rotates photoconductive surface 12 through charging station A. A corona generating device, depicted generally at vl6, extends tranvfersely across photoconductive surface 12. By being positioned in this orientation, corona generating device 16 is capable of charging photoconductivesurface 12 to a relatively high uniform potential. A suitable corona generating" device 16 is described in U.S. Pat. No. 2,778,946 issued to Mayo in 1957.

Thereafter, charged photoconductive surface 12 rotates to exposure station B-which includes thereat a moving lens system, designated generally by the reference numeral 18, and a color filter mechanism, indicated generally at 20. Original document 22 is stationarily supported face down upon transparent platen 24. Lamp assembly 26 and lens system 18 are moved in timed relation with photoconductive surface 12 to produce a flowing light image of the original document on photoconductive surface 12. During exposure, filter mechanism 20 interposes selective color filters into the optical light path of lens 18. The color filter operates on the light passing therethrough to record an electrostatic latent image onphotoconductive surface 12 corresponding to a spectral region of theelectromagnetic wave spectrum, i.e., a color separated latent image.

After the electrostatic latent image has been recorded on photoconductive 12, drum rotates to development station C. Development station C includes three individual developer units generally indicated by the reference numeral 28, 30 and 32, respectively. Each developer unit contains toner particles of a specified color. The developer unit having toner particles appropriate for the filter utilized develops the electrostatic latent image recorded on photoconductor surface 12. Preferably, developer units 28, 30 and 32 are all of a type generally referred to in the art as magnetic brush development units. In a typical magnetic brush development system, a magnetizable developer mix having carrier granules and toner particles is continually brought through a directional flux field forming a brush of developer mix. Development is achieved by bringing the brush of developer mix into contact with photoconductive surface 12. Each of the respective developer units 28, 30 and 32 apply-toner particles corresponding to the complement of the color separated electrostatic latent image recorded on photoconductive surface 12.

Having been developed, the powder image electrostatically adhering to photoconductive surface 12 is advanced to transfer station D. At transfer station D, the powder image is transferred to' a sheet of final support material 34, e.g., plain paper or a thermoplastic transparency amongst others, by means of a biased transfer roll, shown generally at 36. Transfer roll 36 is biased electrically to a potential of sufficient magnitude and polarity to electrostatically attract toner particles from photoconductive surface 12 to support sheet 34. A single sheet of final support material 34 is supported on transfer roll 36. Roll 36 is arranged to move in synchronism with photoconductive surface 12 and is adapted to recirculate support material 34 for a plurality of cycles, i.e., 3 cycles. In this manner successive toner powder images, each corresponding to a specific color in the electromagnetic wave spectrum, are placed in superimposed registration, upon support material 34. Hence, it is apparent, that in this way a multi-color copy is reproduced from the colored original.

Support material 34 is stripped from roll 36 and passed to a fusing'station (not shown) where the powder image is coalesced thereto.

The final processing station in the direction of rotation of drum 10, as indicated by arrow 14, is cleaning station E, A rotatably mounted fibrous brush 38 is positioned at cleaning station E, and is maintained in engagement with photoconductive surface 12 of rotating drum 10. In this way, residual toner particles remaining on photoconductive surface 12 are removed therefrom.

Additional toner particles are. added to the respective developer unit when developability, as hereinbefore sity thereof. Fiber optic light pipe 48 directs the modulated light rays to photosensor 46. Photosensor 46 is mounted within heating apparatus 50 to minimize thermal fluctuations due to temperature variations. Suitable logic circuitry compares the electrical output signal from photosensor 46 with a reference to determine whether or not toner particles should be dispensed to the appropriate developer unit, i.e., yellow toner particles to developer unit 28, magenta toner particles to developer unit 30, cyan toner particles to developer unit 32.

Turning now to FIG. '2, there is shown the detailed construction of regulating apparatus 40. Transparent electrode 42 is'mounted on photoconductive surface 12 in the non-image portion thereof. Electrode 42 includes a glass window 52 having a transparent tin oxide coating thereon. Electrically conductive glass of this nature is made by Pittsburgh Plate Glass under the trademark NESA or by Corning Glass Company under the trademark Electro-Conductive. A generally tubular member threadedly engages an aperture in the circumferential surface of drum l0 and is arranged to align light source 44 mounted therein with glass 52. As shown in FIG. 2, light source 44 is mounted on plate 56 which, in turn, is mounted slidingly in tubular member 54. Plate 56 engages undercut 58 in tubular member 54 and is positioned thereby. Lock screw 60 secures plate 56 in the aforementioned position. Suitable lead wires 62 extend from light source 44 and are interconnected with lead wires 64which pass through the hollow core of shaft member 66. Shaft member 66 is adapted to support drum l0 rotatably. Lead wires 66 are interconnected-to slip ring assembly 68 which transmits a regulated current from voltage regulator 70. Voltage regulator 70 receives an unregulated input of between 8 and 10 volts and adjusts the aforementioned input to a regulated output, preferably, of about 5 volts for exciting lamp 44.

Referring once again to FIG. 2, an electrical biasing voltage is applied to transparent electrode 42 through slip ring 68. Preferably, this voltage simulates the electrostatic latent image recorded on photoconductive surface 12. The voltage is automatically applied to transparent electrode 42 via the position of drum 10 with respect to slip ring assembly 68. Hence, prior to entering the development zone a voltage of about 200 volts above developer bias, which is preferably about 500 volts, is applied to transparent electrode 42. As drum 10 rotates into'the development zone, the magnetic brush assembly of the respective developer unit applies toner particles to transparent electrode 42. Toner particles are attracted to transparent electrode 42 by thevoltage differential of approximately 200 volts between electrode 42 and the corresponding developer unit. The biasing voltage is removed from electrode 42 as it reaches cleaning station E permitting brush 38 to remove the remaining toner particles therefrom. The light rays transmitted through electrode 42 are guided by fiber optic light pipe 48 to photosensor, or photocell 46, disposed within heating apparatus 50. Preferably, glass fiber optics are used to obtain good transmittance in the near infrared region. Glass fiber optics do not attenuate radiant energy in the most sensitive region of the silicon phototransistor, which is the preferred photocell.

Fiber optic light pipe 48 is mounted in plenum chamber 72 by suitable mounting means, e.g., a clamp. Positive lamina flow is directed into the chamber as indicated by arrow 74 to purge the system and reduce particle contamination therein. As shown in FIG. 2, fiber optic light pipe 48 extends into heating apparatus 50 through a heat-tight aperture therein to conduct modulated light rays transmitted through electrode 42 to photosensor 46 mounted therein. Photosensor 46 and the associated circuitelements are all mounted within heating apparatus 50. In this manner, both photosensor 46 and the associate circuit elements are maintained at a temperature ranging from about 50 C to about 60 C, the temperature preferably being about 55 C. This arrangement minimizes thermal fluctuations in the surrounding environment and substantially reduces the system errors due to the temperature sensitivity of photocell 46.

Preferably, photocell 46 is a suitable silicon phototransistor such as that produced by the General Electric Co. Model No. L14B. It should be noted that this type of photocell requires a controlled thermal environment to minimize errors. For example, a 4 C change in temperature in the surrounding environment of photocell 46 will produce an error signal indicating an incorrect concentration of toner particles within the developer mix. Thus, it is highly desirable to maintain the thermal environment of photocell 46 substantially constant. This is accomplished, in the present instance by heating apparatus 50 of the present invention. The foregoing heating apparatus 50 will be described in greater detail with reference to FIGS. 3 through 5, inclusive.

Turning now to FIG. 3, there is shown, in detail heating apparatus 50. Temperature maintaining means or heating apparatus 50 includes an open ended container 74. Container 74 defines an internal chamber 80 for housing photosensor 46 therein. Container 74 is insulated and includes suitable circuitry and heating elements for maintaining interior chamber 80 at a suitable temperature. Control circuitry and heating elements 76 are disposed within container 74. By way of example, a thermistor functioning as one leg of a Wheatstone bridge may be used to detect temperature variations. This type of Wheatstone bridge arrangement may control wire wound resistance heating elements. Wall 78, interposed between the control circuitry and heating elements disposed in internal chamber 80, has a slot 82 therein for receiving a generally planar support member or printed circuit board 84. Disc member 86 is intermeshed with printed circuit board 84 to align lens 88 therein with photosensor 46 mounted on printed circuit board 84. The detailed assembly of disc member 86 with printed circuit board 84 will be described hereinafter with reference to FIGS. 4 and S.

Referring once again to FIG. 3, end cap 90 is secured to container 74 on the open end thereof. End cap 90 is permanently affixed by suitable means, e.g., cement, to the open end of container 74 to form a heat-tight joint therebetween. A plurality of substantially equally spaced protuberances 92 (in this case 8 pins) extend from end cap 90 in a direction substantially parallel to the longitudinal axis thereof. In addition, thereto, end cap 90 includes aperture 94 which is substantially circular to receive end portion 96 of fiber optic light pipe 48. Flanged member 98 includes an aperture 100 therein permitting the fiber optic light pipe 48 to pass therethrough such that end portion 96 extends therebeyond. Moreover, flanged member 98 includes a plurality of equally spaced apertures (in this case 8 holes extending partially therethrough substantially parallel to the longitudinal axis thereof) for receiving pins 92 of end cap 90. Thus, in operation fiber optic light pipe 48 is secured in a heat-tight fashion to flanged member 98 by passing through aperture 100 therein. Fiber optic light pipe 48 is, thereafter, assembled to container 74 by passing end portion 96 slidingly into aperture 94 of end cap 90. Pins 92 mate with holes 94 to form a substantially heat-tight joint therebetween. Hence, in this fashion modulated light rays are guided from transparent electrode 42 to lens 88 which focuses the aforementioned modulated light rays onto photocell 46 for measuring the intensity thereof.

' Turning now to FIG. 4, there is shown an exploded perspective view of disc member 86 being assembled to circuit board 84. As depicted therein, disc member 86 includes substantially circular opening 104 for securing thereto lens 88. Furthermore, disc member 86 includes a slot 106 extending from the circumferential surface thereof partially therethrough being positioned transversely a radius chord thereof. Disc member 86 is adapted to interrnesh with printed circuit board 84. In

order to accomplish this, printed circuit board 84 also By way of example, the aforementioned heating apparatus 50 is arranged to raise the temperature of the internal chamber thereof, wherein photosensor 46 is positioned, from about 60 F to about 55 C within about 3 minutes. Heating apparatus 50 is excited by a suitable 24 volt DC input. The aforementioned control apparatus, hereinbefore described as being proportional, may also be of a suitable on-off type.

Thus, in recapitulation, heating apparatus 50 of the present invention maintains photosensor 46 in a substantially constant thermal environment to substantially minimize temperature fluctuations thereof. In this way, thermal errors induced in the development regulating apparatus are substantially reduced. Moreover, heating apparatus 50 is adapted to permit fiber optic light pipe 48 to pass therethrough and guide the modulated light rays from transparent electrode 42 to photosensor 46. The aforementioned fiber optic light pipe 48 is automatically aligned in heating apparatus 50 with lens 88 to focus the light rays passing therethrough onto photosensor 46.

his, therefore, apparent that there has been provided, in accordance with this invention, an apparatus for minimizing thermally induced errors in a developability regulating apparatus that fully satisfies the objects, aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

What is claimed is:

1. An apparatus for detecting the density of toner particles in an electrophotographic printing machine having a photoconductive member, and a development system arranged to deposit toner particles on an electrostatic latent image recorded on the photoconductive member, including:

transparent electrode means mounted on the photoconductive member spaced from the region of the electrostatic latent image recorded thereon, said electrode means being biased electrically to attract toner particles thereto;

means for illuminating said electrode means, said illuminating means-being mounted on said photoconductive member such that light rays therefrom pass through said electrode means;

means for sensing the intensity of the light rays passing through said electrode means; and

means for maintaining said sensing means at substantially a predetermined temperature to minimize errors in the detecting apparatus resulting from fluctuations in the thermal environment surrounding said sensing means.

2. An apparatus as recited in claim 1, further including a fiber optic light pipe having one end portion thereof mounted exterior to the photoconductive member and closely spaced to said transparent electrode means, said fiber optic light pipe having the other end portion thereof positioned such that said sensing means is in a light receiving relation therewith.

3. An apparatus as recited in claim 2, wherein said sensing means includes a photocell sensitive to thermal fluctuations in the surrounding environment, said pho tocell being located in a light receiving relation with said fiber optic light pipe to receive the light rays transmitted through said electrode means. i

4. An apparatus as recited in claim 3, wherein said temperature maintaining means includes:'

an open ended container defining an internal chamber for housing said photocell; an end cap having an aperture therein adapted to receive the other end portion of said'fiber optic light pipe to form therewith a substantially heat-tight joint, said end cap being mounted to the open end of said container to form therewith a substantially heat-tight joint;

means for heating said container to the predetermined temperature; and

means for controlling said heating means to maintain said container substantially at the predetermined temperature.

5. An apparatus as recited in claim 4, wherein:

said end cap includes a plurality of substantially equally spaced protuberances extending in a direction substantially parallel to the longitudinal axis thereof; and

said fiber optic light pipe includes a flanged member having an aperture therein permitting the other end portion of said fiber optic light pipe to pass therethrough and extend therefrom forming a substantially heat-tight joint therewith, said flanged member having a plurality of substantially equally spaced openings therein arranged to receive said protuberances extending from said end cap.

6. An apparatus as recited in claim 5, wherein the predetermined temperature ranges from about 50 C to about 60 C, preferably being about 55 C. 

1. An apparatus for detecting the density of toner particles in an electrophotographic printing machine having a photoconductive member, and a development system arranged to deposit toner particles on an electrostatic latent image recorded on the photoconductive member, including: transparent electrode means mounted on the photoconductive member spaced from the region of the electrostatic latent image recorded thereon, said electrode means being biased electrically to attract toner particles thereto; means for illuminating said electrode means, said illuminating means being mounted on said photoconductive member such that light rays therefrom pass through said electrode means; means for sensing the intensity of the light rays passing through said electrode means; and means for maintaining said sensing means at substantially a predetermined temperature to minimize errors in the detecting apparatus resulting from fluctuations in the thermal environment surrounding said sensing means.
 2. An apparatus as recited in claim 1, further including a fiber optic light pipe having one end portion thereof mounted exterior to the photoconductive member and closely spaced to said transparent electrode means, said fiber optic light pipe having the other end portion thereof positioned such that said sensing means is in a light receiving relation therewith.
 3. An apparatus as recited in claim 2, wherein said sensing means includes a photocell sensitive to thermal fluctuations in the surrounding environment, said photocell being located in a light receiving relation with said fiber optic lIght pipe to receive the light rays transmitted through said electrode means.
 4. An apparatus as recited in claim 3, wherein said temperature maintaining means includes: an open ended container defining an internal chamber for housing said photocell; an end cap having an aperture therein adapted to receive the other end portion of said fiber optic light pipe to form therewith a substantially heat-tight joint, said end cap being mounted to the open end of said container to form therewith a substantially heat-tight joint; means for heating said container to the predetermined temperature; and means for controlling said heating means to maintain said container substantially at the predetermined temperature.
 5. An apparatus as recited in claim 4, wherein: said end cap includes a plurality of substantially equally spaced protuberances extending in a direction substantially parallel to the longitudinal axis thereof; and said fiber optic light pipe includes a flanged member having an aperture therein permitting the other end portion of said fiber optic light pipe to pass therethrough and extend therefrom forming a substantially heat-tight joint therewith, said flanged member having a plurality of substantially equally spaced openings therein arranged to receive said protuberances extending from said end cap.
 6. An apparatus as recited in claim 5, wherein the predetermined temperature ranges from about 50* C to about 60* C, preferably being about 55* C. 